Generally, a mobile communication terminal such as a cellular phone, a pager and a PDA employs a vibration device in order to generate vibration in addition to a sound signal such as bell sound to a user when a call or a message is received.
FIG. 1 is a sectional view showing a conventional vibration device, and FIG. 2 is a perspective view showing a leaf spring used in the conventional vibration device.
As shown in FIG. 1, the conventional vibration device includes a lower case 20, a coil 30 mounted at the center of the lower case 20, a circuit board 80 for applying power from outside, a spring holder 70 formed around the outer circumference of the lower case 20, a leaf spring 60 insert-molded to the spring holder 70, a vibrating member 90 elastically supported by the leaf spring 60, and an upper case 10 having a cap shape.
The vibrating member 90 includes a weight 50 with a predetermined weight, and a magnet 40 mounted in a groove formed in a lower surface of the weight 50, and the vibrating member 90 is fixed to the leaf spring 60.
The leaf spring 60 has three fixing legs 62, which are twisted in a pinwheel shape at a ring-shaped loop having a central hollow so that the weight 50 may be combined to an upper portion thereof as if it is inserted therein. An end 61 of the fixing leg 62 is combined with the spring holder 70.
The conventional vibration device configured as above is operated as below. If an external power is applied to the coil 30 through the circuit board 80, a magnetic flux is generated in the coil 30. By means of interaction between the magnetic flux generated in the coil 30 and the magnetic flux of a magnet 40 faced with the coil 30, the vibrating member 90 is vibrated vertically.
The vertical vibration of the vibrating member 90 is transferred to the leaf spring 60, and the vibration transferred by elasticity of the leaf spring 60 is then transferred to the spring holder 70 and the cases 10 and 20, and then to outside.
However, as a mobile communication terminal becomes smaller, the overall size of the vibration device mounted in the mobile communication terminal should be reduced. Accordingly, the weight 50 which directly generates vibration becomes also lighter together with decreasing an outer diameter, so a vibrating amount is also decreased.
Thus, in order to solve this problem, there was an attempt to reduce a size of the magnet 40 and increase a thickness of the weight 50 instead for increasing the vibrating amount.
However, if the weight 50 becomes thicker, the size of the magnet 40 is reduced though a weight of the weight 50 is increased, so the vibrating amount caused by the interaction between the magnet 40 and the coil 30 is even decreased.
In addition, if the weight 50 is enlarged in a circumferential direction in order to increase a vibrating amount, a length of the leaf spring 60 formed between the weight 50 and the spring holder 70 is reduced, thereby decreasing an elastic force. This also decreases a vibrating amount.
Thus, there is an urgent need for a new vibration device which may increase a vibrating amount with a smaller size.